If the human transport device is an escalator, a transport belt is thus formed as an endless step belt from a plurality of steps as tread elements. If the human transport device is a travellator, a transport belt is thus formed as an endless pallet belt from a plurality of pallets as tread elements.
If the human transport device is an escalator, the first return station is usually disposed on a first building floor plane and the second return station is usually disposed on a second building floor plane, wherein the second building floor plane lies higher or lower in relation to the first building floor plane. The human transport device in this case thus has an upper return station and a lower return station. In this case, it is in particular usual that the upper return station for driving the step belt of the escalator is connected to the drive unit by way of a gearbox. If the human transport device is a travellator, a front return station and a rear return station are usually provided as the first return station and the second return station, respectively.
The transport region of the human transport device is that region in which users of the human transport device are transported, thus in particular that region that can be walked on by users. By contrast, the return region of the human transport device is usually that region in which the tread elements are returned back to the beginning of the transport region again, and which is usually not visible to the users. However, the reversal of direction in the case of some human transport devices is performed horizontally such that the return region is disposed in the same plane as the transport region. In such cases, the return region is also used for the transport region, the return region in these cases thus moreover being a transport region.
The tread elements in the transport region and return region to this extent have opposite directions of movement. The respective change in the direction of movement of the tread elements from the transport region to the return region and from the return region to the transport region herein is implemented by the return stations.
In the operation of a human transport device, a breakage of a tread element or breakage of a holding element or of a track roller of the tread element can in particular lead to a faulty arrangement of a tread element. A faulty arrangement of a tread element herein leads in particular to the tread element being lowered or released from the transport belt and thereby can result in the transport belt being interrupted, in particular opened. Since such a faulty arrangement of a tread element represents a risk potential both for the faultless further operation of the human transport device as well as for the users of the human transport device, an early identification of such a faulty arrangement is of importance.
It is known for monitoring apparatuses to be used for identifying a faulty arrangement of a tread element. For example, if a breakage of a tread element is identified by means of the monitoring device, the human transport device can be taken out of operation.
A monitoring apparatus for identifying breakages in steps in the case of escalators is known, for example from the publication JP 08169679 A. Images of the steps are acquired by photo technology herein. The acquired images are subjected to a comparison with images of faultless steps in order for a fault to be detected. This monitoring herein is technically complex to implement and is thus cost-intensive. Moreover, correct monitoring is no longer provided in the case of a contamination of the camera lens.
Furthermore, a monitoring apparatus for a transport means, in particular for an escalator having an inclined step belt, guided on chains, and having endlessly revolving steps, is known from DE 42 19 073 A1. The monitoring apparatus herein comprises a light barrier wherein the light beam of the light barrier runs at a tight spacing below the steps of the step track and is directed so as to be parallel with the direction of movement of the step track. The drive of the step track is switched off as soon as an interruption of the light beam takes place on account of a step being lowered. A disadvantage of the monitoring apparatus proposed lies in that it is not uncommon for an interruption of the light beam to take place for other reasons than that of a step being lowered. In particular, an interruption of the light beam can be caused by the ingress of foreign matter such as leaves or trash, or else by dust or small animals such as insects. Correct monitoring is no longer provided in this instance.
Thus a need exists for a human transport device with a view to a faulty arrangement of a tread element such as, in particular, a lowered step, being identified in a more reliable manner. The identification of a faulty arrangement herein should advantageously moreover be implementable in a cost-effective manner.